The present invention relates to gas transmission assemblies. More particularly, it relates to gas risers used in transmitting natural gas from a buried underground gas line to a home or business.
U.S. Pat. No. 5,590,914 is commonly owned by the assignee of the present application and the details of that patent are incorporated herein by reference. It generally illustrates a prior art gas riser assembly of the type to which the subject invention pertains where natural gas is supplied from a main, through a buried service line, and eventually to the riser assembly. The riser assembly extends from an underground connection with the service line, through an elbow region, to a vertically disposed pipe that communicates with a manifold of an above-ground gas meter.
The prior art gas riser assembly includes a double-walled conduit comprising an inner, plastic tube or casing received inside a rigid, outer casing. The inner casing defines the fluid passage for the gas as it is transported from the service line to the manifold. The riser assembly is connected to the manifold in a fluid tight manner so that a sealed passageway is provided from the underground connection with the service line to the manifold.
Strength of the riser is an important consideration. It must be strong enough to support the weight load of the residential piping system, while maintaining a sealed relationship with the manifold. It is also preferred that the assembly be electrically isolated from ground contact. Additionally, it is desirably to use corrosion-free material in the riser assembly since the outer casing, which is typically made of steel, is otherwise subject to corrosive attack. For this reason the outer casing is usually treated, i.e., coated, to prevent corrosion.
One problem with prior riser assemblies is the degradation of the coating material prior to installation. Risers are typically stored loosely in installation vehicles for days, even weeks at a time. During this time the riser may easily be subjected to collision with other objects in the storage area. These collisions may undesirably damage or weaken the anticorrosive coating, creating an increased likelihood of corrosion at or near the areas of impact.
Thus, there is a desire for a new and improved riser assembly that overcomes the foregoing difficulties and others while producing better and more advantageous overall results. The new and improved riser assembly should be corrosion resistant, durable, isolated from electrical ground contact, and strong enough to support the weight load of residential piping assembly resulting in an extended service life.